Method of reclaiming tungsten carbide tool bits

ABSTRACT

A method of separating a used tungsten carbide tool bit from a steel tool holder wherein the bit is bonded to the holder by means of a copper-silver alloy by dissolving out the alloy in an acid-water solution consisting preferably of about 47 volume percent nitric acid at room temperature.

United States Patent Korpak 1 51 Jan. 18, 1972 [54] METHOD OF RECLAIMINGTUNGSTEN CARBIDE TOOL BITS [72] inventor: Charles Korpak, Union Lake,Mich.

[73] Assignee: General Motors Corporation, Detroit,

Mich.

[221 Filed: Aug. 22, 1969 21 Appl. No.: 852,489

52 0.8. (:1 ..29/426 511 mu ..B23p 19/00 [58] Field of Search ..29/426,401; 76/108; 134/3,

Primary Examiner-Charlie T. Moon Att0rneyWilliam S. Pettigrew and PeterP. Kozak [5 7] ABSTRACT A method of separating a used tungsten carbidetool bit from a steel tool holder wherein the bit is bonded to theholder by means of a copper-silver alloy by dissolving out the alloy inan acid'water solution consisting preferably of about 47 volume percentnitric acid at room temperature.

2 Claims, No Drawings METHOD OF RECLAIMING TUNGSTEN CARBIDE TOOL BITSThis invention relates to the reclamation of tungsten carbide tool bitsand, more particularly, to a method of separating used tungsten carbidetool bits which are bonded to steel holders by means of a copper-silveralloy from their holders.

A common tool in use today in machining operations is a steel tool witha tungsten carbide cutting bit. Tungsten carbide is particularlyapplicable in machining operations, particularly in machining castirons, because of its ability to withstand high impact stresses, hightemperatures, and wear. However, because tungsten carbide is veryexpensive it is only used for the cutting edge of the tool and,therefore, in the manufacture of cutting tools of this type, tungstencarbide bits are formed in the shape of a cutting edge and then bondedto a more inexpensive material such as steel which is strong, durable,and can support the carbide tip. Commonly, the bit is bonded to thesteel holder by means of a copper-silver alloy which is heated and thenapplied between the carbide tip and the steel holder thus fastening thebit to the holder.

One of the most expensive parts of any machining operation is themaintenance of a clean, sharp cutting edge on the tool. Because tungstencarbide bits are expensive, it is desirable to be able to recover thesebits from their holders so that they may be reformed into a sharp edgeand then rebonded to steel holders for further use. The present methodfor separating these carbide tips from their steel too] holders is toplace the tool in an arc furnace which is heated up to a hightemperature for a relatively long period of time in order to break thecopper-silver alloy bond between the bit and the tool holder. Since thisbond is very strong, it takes a relatively large amount of heat to causeseparation. In this method, the furnace temperature is very near theliquation point of the alloy which presents a problem of temperaturecontrol so as to break the bond without overheating the bits and fusingthem to their holders. This method of furnace separation has a number ofdisadvantages including lack of control of the temperature, thepossibility of excessive heating and fusing of the tip to the steelholder, the relatively long times involved in separation, the relativelyhigh cost involved, the inability to have complete separation of thebits in mass quantities due to uneven heating, and the possible hazardsinvolved in loading and unloading tools from a heated furnace.

Accordingly, it is the principle object of this invention to provide animproved and more efficient method of separating tungsten carbide toolbits from their steel tool holders than has heretofore been available. 1

A further object of this invention is to provide a controlledenvironment in which the bits may be separated quickly and efficientlyon a mass scale.

These and other objects can, surprisingly, be realized by providing anacid-water solution consisting of from 31 to 70 volume percent nitricacid, preferably 47 volume percent, at a temperature of from 40 to 90F., preferably at room temperature, and then immersing the tools in thesolution for a time sufficient for the solution to completely dissolvethe alloy whereby the bits separate from their holders. It has beenfound that tools with the normal amount of bonding alloy present intools of this type could be completely separated in from 2 to 6 hoursand that the solution could be used for up to three to four times. Ithas been further found that the life of the solution could be increasedby first removing oil, grease, and dirt from the tools with atrichloroethyl solution before immersing the tools in the acid solution.After the bonding alloy is completely dissolved in the solution and thebits have been separated from their holders, the bits and holders areremoved from the solution and water rinsed. The tungsten carbide bitsmay now be reformed by well-known processes into sharp cutting bits andrebonded to the tool holders for further use. After three to four runsthe spent solution has a relatively heavy trace of copper and silver,some of which may be recovered by electrolytic deposition of the nitricsolution. When operating under the process set forth herein, acontrolled reaction takes place in which the alloy bond is completelydissolved in a sufficiently short time for the process to be economicalbut without damage to either the tungsten carbide bits or the steel toolholders.

The various limits set forth in this invention are critical to theprocess and yield a quite unexpected result. One would normally expectthat a nitric acid solution of strength sufficient to dissolve thecopper-silver bond would cause a violent reaction with the steel toolholders and subsequent damage sufficient to render them unusable.However, a nitric acid solution in the range of 31 to 70 volume percentwith the optimum being about 47 volume percent yields a controlledreaction wherein the alloy bond is completely dissolved with only minorattack on the steel which yields the beneficial result. of polishing theholders. If the solution falls below 3l percent a violent reaction takesplace in which the steel is attacked and if the solution is above 70percent dissolution of alloy does not take place. Temperature control inthe range of 40 to F. is also necessary in order for the reaction toproceed as desired. Too low a temperature substantially retards thereaction while too high a temperature causes a violent and undesiredreaction. It has been found that optimum results can be achieved whenthe acid-water solution is at about room temperature and consists ofabout 47 volume percent nitric acid.

A further condition critical to the invention is that the minimum ratioof the weight of the solution to the weight of the tool is 1.25: l .0.If this ratio falls below the minimum, then a violent and undesirablereaction will take place in which the holders are attacked.

The invention will be more particularly described in the examples whichfollow. The examples are merely illustrative of the parameters of thisinvention and set forth an operative process.

EXAMPLE I Fourteen pounds of commercial grade nitric acid is dissolvedin 7 pounds of water to form about a 47 percent nitric acid solution.The solution is then allowed to set in order to dissipate the heat ofthe reaction and be in equilibrium with the room temperature of about72-75 F. Fourteen pounds of used tools are placed in the solution withcomplete dissolution of the bonding alloy and separation of the toolsoccurring in about 4 hours. The ratio of the weight of solution to theweight of tools was 1.5 :l and the solution was good for five runs or 70pounds of tools.

EXAMPLE II The same procedure as example I was followed except that theconcentration of the solution was increased to about 53 percentoccurring after about 6 hours. The solution-tool ratio was 2: 1.

Thus having described the invention, what is claimed is:

l. A method of separating the assembly comprising a tungsten carbide bitand a steel tool holder wherein said bit is bonded to said holder bymeans of a copper-silver alloy, said method comprising placing saidassembly in a nitric acidwater solution consisting of from 31 to 70volume percent nitric acid at a temperature of from 40 to 90 F. for atime sufticient for said solution to completely dissolve said alloywhereby said bit separates from said holder, the ratio of the weight ofsaid solution to the weight of said assembly being a minimum of1.25:1.0.

2. The method of claim 1 wherein said solution consists of about 47volume percent nitric acid at a temperature of from 72 to 75 F.

Po-wso f UNITED STATES PATENT OFFICE- CERTIFICATE OF CORRECTION Patent3,634,923 Dated January 18, 1972 ln w' l v Charles Korpak It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2. line 55, after "peroent" insert with separation T Signedand'sealed this. 11th day of July 1972.v

(SEAL) Attest:

EDWARD MELETCHEI JBJ v. mBERT GOTTSCHALK Attesting' OfficereCommissioner of Patents

2. The method of claim 1 wherein said solution consists of about 47volume percent nitric acid at a temperature of from 72* to 75* F.